a. Field of the Invention
The present invention relates broadly to a coupling of the type which is telescopically engaged with the end of a pipe. In particular, the invention has regard to an improved coupling of this type having locking apparatus which rigidly locks the coupling and pipe together against relative axial movement.
B. Description of the Prior Art
U.S. Pat. No. 3,704,033 discloses a coupling having locking apparatus in the form of a single set of gripping elements or slips where the slips are disposed in side-by-side circumferential relationship to encircle the pipe. Each slip in turn includes a pair of oppositely tapered surfaces mateably engaged with a pair of axially and oppositely tapered surfaces of an annular bowl assembly; one tapered bowl surface being movable axially towards the other tapered bowl surface, which is stationary in this case, to cam the slips radially inward towards gripping engagement with the pipe whereby the coupling and pipe are locked together against relative axial movement. More particularly, the double tapered configuration between the slips and bowl assembly serves to procure resistance to axial tension and compression forces between the coupling and pipe to lock them together. Under certain circumstances however, it has been found that this particular form of locking apparatus does not resist large axial forces imparted to the coupling and pipe. It is believed that this a result of the bowl assembly not moving the slips into uniform and firm gripping engagement with the pipe. That is to say, it is believed that because only one tapered bowl surface is movable to set the slips, the slips do not achieve their optimum set position and, hence, are unable to resist large tension and compression forces which may be imparted to the coupling and pipe.